In the double_plant.json file at \assets\minecraft\models\ folder, the variants of 'sunflower_bottom', 'grass_top', and 'rose_top' seem to be messed up. The 'sunflower_bottom' variant is being used on both the bottom of a sunflower, the top of a double tall grass, and the top of the double red rose. The 'grass_top' variant seems to be unused, but i haven't tried making custom meshes on the other double plants so i'm not sure if it is used over onto a different plant. If the 'grass_top' variant isn't being used, the 'rose_top' variant most likely isn't being used either. I'm not sure if that is all of the mix-ups in that file too, i haven't tried changing anything else for a texture pack.